After arbitrary bio size is supported, the incoming bio may
be very big. We have to split the bio into small bios so that
each holds at most BIO_MAX_PAGES bvecs for safety reason, such
as bio_clone().
This patch fixes the following kernel crash:
> [ 172.660142] BUG: unable to handle kernel NULL pointer dereference at
> 0000000000000028
> [ 172.660229] IP: [<ffffffff811e53b4>] bio_trim+0xf/0x2a
> [ 172.660289] PGD 7faf3e067 PUD 7f9279067 PMD 0
> [ 172.660399] Oops: 0000 [#1] SMP
> [...]
> [ 172.664780] Call Trace:
> [ 172.664813] [<ffffffffa007f3be>] ? raid1_make_request+0x2e8/0xad7 [raid1]
> [ 172.664846] [<ffffffff811f07da>] ? blk_queue_split+0x377/0x3d4
> [ 172.664880] [<ffffffffa005fb5f>] ? md_make_request+0xf6/0x1e9 [md_mod]
> [ 172.664912] [<ffffffff811eb860>] ? generic_make_request+0xb5/0x155
> [ 172.664947] [<ffffffffa0445c89>] ? prio_io+0x85/0x95 [bcache]
> [ 172.664981] [<ffffffffa0448252>] ? register_cache_set+0x355/0x8d0 [bcache]
> [ 172.665016] [<ffffffffa04497d3>] ? register_bcache+0x1006/0x1174 [bcache]
Fixes: 54efd50(block: make generic_make_request handle arbitrarily sized bios)
Reported-by: Sebastian Roesner <sroesner-kernel...@roesner-online.de>
Reported-by: Eric Wheeler <bca...@lists.ewheeler.net>
Cc: sta...@vger.kernel.org (4.2+)
Cc: Shaohua Li <s...@fb.com>
Signed-off-by: Ming Lei <ming....@canonical.com>
---
I can reproduce the issue and verify the fix by the following approach:
- create one raid1 over two virtio-blk
- build bcache device over the above raid1 and another cache device.
- set cache mode as writeback
- run random write over ext4 on the bcache device
- then the crash can be triggered
block/blk-merge.c | 12 ++++++++++++
1 file changed, 12 insertions(+)
diff --git a/block/blk-merge.c b/block/blk-merge.c
index 2613531..9a8651f 100644
--- a/block/blk-merge.c
+++ b/block/blk-merge.c
@@ -79,6 +79,18 @@ static inline unsigned get_max_io_size(struct request_queue
*q,
/* aligned to logical block size */
sectors &= ~(mask >> 9);
+ /*
+ * With arbitrary bio size, the incoming bio may be very big.
+ * We have to split the bio into small bios so that each holds
+ * at most BIO_MAX_PAGES bvecs for safety reason, such as
+ * bio_clone().
+ *
+ * In the future, the limit might be converted into per-queue
+ * flag.
+ */
+ sectors = min_t(unsigned, sectors, BIO_MAX_PAGES <<
+ (PAGE_CACHE_SHIFT - 9));
+
return sectors;
}
--
1.9.1
